Aerial Vehicle and Method of Flight

ABSTRACT

An aerial vehicle is described which comprises:
         a first compartment for holding a lighter than air gas;   a second compartment for holding atmospheric air and having an inlet and an outlet;   a solar panel for converting sunlight into electricity;   a compressor for pumping atmospheric air through the inlet into the second compartment;   control means for controlling the pitch and yaw of the vehicle; and
 
a controller for controlling the buoyancy of the vehicle via the compressor and the outlet such that the vehicle is either lighter than the surrounding air and rising or heavier than the surrounding air and falling, and for controlling the control means such that the rising and falling motion includes a horizontal component.
       

     In another embodiment the solar panel is replaced by an engine and a fuel tank for storing fuel for the engine is also provided. 
     The aerial vehicle can remain airborne for extended periods by using buoyancy propulsion. 
     In the embodiments including a solar panel, a system including a light transmission station may be provided to supply energy to the solar panel from the light transmission station rather than relying on the incident sunlight alone. 
     A method of flight using buoyancy propulsion is also described.

The present application relates to an aerial vehicle. More particularlyit relates to an aerial vehicle and method of flight in which thevehicle is propelled by altering the buoyancy of the vehicle and usingthe resulting rising and falling motion to produce a horizontal motioncomponent.

Aerial vehicles require some means to maintain their altitude. At abasic level aerial vehicles can be considered as those that are lighterthan air and those that are heavier than air. An example of a lighterthan air vehicle is a blimp, which maintains its altitude by buoyancy.An example of a heavier than air vehicle is a glider, which gainsaltitude on thermals and then glides down to lower altitudes using airspeed to generate lift from the passage of air over its wings andcontrol surfaces.

Unlike powered flight, where fuel must be expended to generate lift,both blimps and gliders can maintain altitude for reasonably longperiods because no fuel is expended to maintain lift. Nevertheless, thetime that they can spend airborne is still limited. A glider must find asource of lift such as a thermal, otherwise it will eventually glidedown to the ground. Blimps are maintained in the air by the buoyancy ofa lighter than air gas, such as helium, in an envelope. Over time thelighter than air gas will escape from the envelope and the blimp mustland to refill the envelope or refuel to propel the vehicle throughwind.

Recently there has been a desire to develop aerial vehicles that canremain airborne for long periods: several days and longer. Such vehiclesare useful for gathering reconnaissance and relaying communications.Conventional aircraft are not suitable for remaining airborne forseveral days. A glider cannot remain airborne long enough to be useful.A blimp has limited longevity in such applications because the lighterthan air gas in its envelope will gradually escape. The blimp must alsobe driven by a propeller to maintain position against winds and aircurrents and the required energy and supply of fuel limits the time aposition can be maintained, even if the blimp is still airborne.Although blimps may be tethered in position this requires access to theground under the reconnaissance position, something which may not bepossible.

Specialist vehicles that can remain airborne for up to three days areknown. For example, QinetiQ has demonstrated the Zephyr aircraft. TheZephyr is a lightweight, heavier than air, powered aircraft that usessolar cells on its wings to charge a rechargeable battery. The Zephyrflies using the thrust from propellers powered by the battery and theresulting aerodynamic lift from its wings as it moves through the air.In tests, the Zephyr has demonstrated a continuous unmanned flight oftwo weeks.

The length of time the Zephyr can remain airborne is determined by theenergy budget—the energy required to power the propellers to maintainaltitude and position versus the energy generated by the solar cells. Tominimise the energy required to maintain altitude and position, theZephyr moves at relatively slow speeds. To minimise drag the solar cellsare mounted on the surface of the wing. However, this introduces adisadvantage because they may not be orientated in the optimum positiontowards the sun to gather the most incident sunlight.

Buoyancy propelled sea vehicles are known. These include the Seagliderdeveloped by the University of Washington, the SLOCUM glider developedby the University of Princeton and the Spray glider developed withsupport from the US office of Naval Research. These vehicles arepropelled by changes in their buoyancy causing them to be alternatelyheavier than the surrounding water and sinking or lighter than thesurrounding water and rising.

The density change cycle is powered by the thermal gradient between deepwater and surface water, in other words it is indirectly powered by theenergy input of the sun warming the surface water. Buoyancy powered seavehicles can remain in use for many months, essentially limited by theelectrical supply for their sensors and navigation systems. Existing seabuoyancy powered sea vehicles cannot easily be adapted for use in air.Atmospheric air does not demonstrate the same temperature gradient (itis colder rather than warmer at altitude). There are other problems too,the increased density of water compared with air means the overalldensity of the craft can be much higher for use in water than is neededfor use in air. Known sea vehicles using buoyancy propulsion may have amass as high as 50 kg. This helps them to be less effected by oceancurrents than the effect of atmospheric winds on a lighter than airaerial vehicle. The vehicles also move slowly, with a horizontal speedof 0.4 m/s, limiting their ability to traverse distances quickly.

A buoyancy propelled aerial vehicle is discussed in WO-A-2005/007506(Hunt). Hunt proposes to change an aircraft's density by a phase changetechnique, changing a gas into a liquid state and vice versa. However,Hunt's aircraft proposes to generate the power for this phase changeusing wind turbines. Although he discusses that the wind turbines can beused to store energy while the vehicle is on the ground, once thevehicle is in flight no additional energy can be input to the systembecause the energy to drive the wind turbines comes from thegravitationally driven motion of the craft. The endurance is determinedby the stored energy from the turbines before the craft takes off. Inflight it is impossible for the gravitational cycle to generate enoughenergy to power further gravitational cycles indefinitely without anexternal input of energy, otherwise the vehicle would be a perpetualmotion machine.

It would be desirable to overcome at least one of the disadvantages withexisting aerial vehicles. Accordingly, the present invention provides anaerial vehicle which is propelled by changing its buoyancy bycompressing atmospheric air into a compartment of the vehicle. Thecompressed air acts as ballast so that the vehicle is either heavierthan air and falling or lighter than air and rising when compressed airis expelled. As it rises and falls a control mechanism is actuated tocreate a horizontal component to the motion, for example through a wingor flight surfaces. As is discussed below such a method can producesurprising horizontal speed in air and can be more energy efficient thangenerating thrust with a propeller, enabling a longer time in the air.

According to the present invention, there is provided an aerial vehiclecomprising:

a first compartment for holding a lighter than air gas;

a second compartment for holding atmospheric air and having an inlet andan outlet;

a solar panel for converting sunlight into electricity;

a compressor for pumping atmospheric air through the inlet into thesecond compartment;

control means for controlling the pitch and yaw of the vehicle; and

a controller for controlling the buoyancy of the vehicle via thecompressor and the outlet such that the vehicle is either lighter thanthe surrounding air and rising or heavier than the surrounding air andfalling, and for controlling the control means such that the rising andfalling motion includes a horizontal component.

The first compartment filled with lighter than air gas enables thevehicle to have an overall weight lighter than the surrounding air (inother words the vehicle weighs less than the volume of air itdisplaces). It has been found that for use in air relatively smallchanges in the weight of the vehicle can alter its balance between beinglighter than air or heavier than air. Thus, the buoyancy of the vehiclecan be controlled simply by compressing air into the second compartment.This is simpler and requires less energy than the phase change techniqueproposed by Hunt. The external energy to alter the buoyancy is providedby an external source, the solar panel. If it is desired for the vehicleto operate during the night when the sun is not available, batteries maybe included to store the energy for use at night.

Preferably the horizontal component of the rising and falling motion isgreater than the vertical component. The horizontal component may besufficiently large that the overall motion of the vehicle issubstantially horizontal.

The first and second compartments may be any envelope suitable forretaining a gas. The solar panel may be any arrangement suitable forgenerating electricity from incident sunlight. Preferably, a solar cellsuch as photovoltaic cell is used but other solar energy systems mayalso be used including the photoelectric effect and solar furnaces. Thecompressor may be any pump suitable for compressing air, for example itmay comprise an air pump driven by an electric motor. The control meanscan be any suitable control system for controlling the pitch, roll andyaw of the vehicle, some non-limiting examples are discussed later inthis specification.

The controller may be a microprocessor, microcontroller, fieldprogrammable gate array, application specific integrated circuit, or anyother suitable device. The controller preferably includes interfaces forsensors to allow control of the aircraft, for example including aposition sensor, attitude sensor, compass, pressure sensors, infraredand/or further sensors. IR sensors can be orientated in the XYZ axes todetermine the orientation using the property that the IR reading isgenerally warmer towards the ground than the sky.

It has been found that the efficiency of an aerial vehicle according tothe invention is improved, compared with conventional methods ofpropulsion such as a propeller. For example, the vehicle may experiencea free lift force of around 7N/s at sea level launch reducing to 4N/s atthe bottom of a typical operating altitude range (1 km). The forcecontinues to reduce with altitude up to a buoyancy ceiling, for example3.5 km. The vehicle may take typically take 10 minutes to ascend from 1km to 3 km. The controller then activates the compressor and air ballastgradually builds up in the second compartment. For example, this mayresult in a constant force of up to 4N arising from gravity during agliding descent for a further 10 minutes. When ballast is expelled aconstant freelift force of 4N applies in gliding ascent. The forcereduces over a further 10 mins as the vehicle approaches its buoyancyceiling, typically providing 2400N/s of force over this cycle (averaging2N). Although the forces are small, the force can be harnessed to resultin unexpectedly fast horizontal motion.

To give an example, an electric motor may power an air pump to draw inand compress atmospheric air to create ballast. If the air pump were todrive a propeller an air speed of around 15 kms/hr would result.However, with this arrangement an airspeed of around 50 kms/hr may berealised (75 kms/hr at a gliding ascent of 16° ascent, 21° glidingdescent) and energy is only consumed for around half the cycle (around100 watts while the motor is in operation to compress air to giveballast for the descent). This gives sufficient ground speed topenetrate wind (other than the most extreme winds) to maintain aloitering position over an operating station.

A preferred operating altitude range is 1-3 km. This operating altituderange may be significantly higher in some embodiments. The vehicle mayalso operate at a higher operating range by launching the firstcompartment semi inflated. As the density changes, the envelope willbecome fully inflated at the required lower operating altitude. A largerfirst compartment may also be used. The vehicle may utilise jet-streamsat around 10 kms-14 ms altitude to traverse distances more quickly ifthe wind offers a useful vector, or alternatively it can circle toutilise thermals as well as using also ridge lift or wave lift.

In another aspect of the invention, an aerial vehicle is provided whichcomprises:

a first compartment for holding a lighter than air gas;

a second compartment for holding atmospheric air and having an inlet andan outlet;

an engine;

a fuel tank for storing fuel for use by the engine;

a compressor for pumping atmospheric air through the inlet into thesecond compartment;

control means for controlling the pitch and yaw of the vehicle; and

a controller for controlling the buoyancy of the vehicle via thecompressor and the outlet such that the vehicle is either lighter thanthe surrounding air and rising or heavier than the surrounding air andfalling, and for controlling the control means such that the rising andfalling motion includes a horizontal component.

The construction of this aspect is therefore the same the first aspect,except that the solar panel is replaced with an engine and fuel tank. Ithas been found that the high efficiency of buoyancy propulsion can beadvantageous when the vehicle is provided with a conventional engine andfuel source. This may allow carrying of heavier loads than with a solarpanel. A buoyancy propelled aerial vehicle consumes less fuel comparedwith a lighter than air blimp or fixed wing aircraft propelled forwardsby a propeller. For example, the buoyancy aerial vehicle may be scaledto carry an ISO container.

In both of the above aspects, the aerial vehicle preferably createssubstantially no aerodynamic lift at a zero degree angle of attack.Ideally, the airframe of the vehicle as a whole has a coefficient oflift which is between approximately −0.01 and 0.01 based on planformreference area.

The control means may be further for controlling the roll of thevehicle.

The aerial vehicle may further comprise a nacelle, and wherein the firstcompartment and the second compartment are both contained within thenacelle. A nacelle is a streamlined enclosure that enables the drag ofthe vehicle to be reduced by housing components inside the nacelle. Asthe forces involved are relatively small, reducing drag can have asignificant effect on the performance of the vehicle.

Preferably, the nacelle has an outer surface which defines a body ofrevolution or an aerofoil. Although the nacelle may have the shape of anaerofoil, it has been found that, surprisingly, the performance may beimproved if the nacelle is shaped such that no (or minimal) aerodynamiclift is generated at a zero angle of attack. A conventional asymmetricalaerofoil commonly used for a wing, will create vortex induced drag as aresult of generating aerodynamic lift. The induced drag is significantand will significantly slow the vehicle. The aerodynamic lift from theaerofoil is not required in a vehicle according to the presentinvention, its lift is generated by the buoyancy of the lighter than airgas in the first compartment. If an asymmetrical aerofoil is used,performance may be improved by orientating the aerofoil such that itgenerates a downward force, rather than a conventional upward, liftforce in gliding ascent.

It will be appreciated that all the components of the vehicle, apartfrom the control surface, could be situated inside the nacelle, orinside additional nacelles, to further reduce the drag on the vehicle.In embodiments including a solar panel, it is particularly advantageousif the nacelle is transparent and the solar panel is contained withinthe nacelle. This enables the solar panel to be oriented moreefficiently towards the sun, without increasing drag.

The efficiency of the solar panel can be further improved in oneembodiment by providing a parabolic mirror associated with the solarpanel for focussing sunlight onto the solar panel. This has severaladvantages. A mirror can weigh less than a solar panel, allowing moresunlight to be gathered for less weight. The cost of providing themirror is also likely to be less than the cost of solar panels ofequivalent area. This embodiment is particularly effective when thesolar panel and mirror are contained within a transparent nacellebecause then the mirror has no effect on the drag. Any suitable mirroredfilm can be used for the parabolic mirror, preferably one that is UVstabilised. In one embodiment 3M Vikuiti Reflection Film, commerciallyavailable from Optical Systems, 3M, 3M Center, St. Paul, Minn.55144-1000 USA is used. It may be manufactured to the requiredthickness, preferably around 10 μm, and provided with a UV stabilisedantireflective coating. This has a reflectance of 95%.

The aerial vehicle may further comprise an electric motor for changingthe orientation of the solar panel and/or the parabolic mirror relativeto the vehicle. This allows the solar panel to track the sun through thesky for improved efficiency and is particularly advantageous when thesolar panel is inside a transparent nacelle because it then has noeffect on drag. Preferably, the orientation may be altered along an axisrunning from the front to the back of the vehicle. The mirror and/orsolar panel may be constructed to have constant distribution of weightabout this axis, so that changing orientation does not alter the weightdistribution of the vehicle. Alternatively, any change in weightdistribution may be compensated through the control surface or by movinginternal components to change the centre of gravity/buoyancy. Thetracking can be implemented simply by monitoring the output of the solarpanel, by using a light sensor or alternatively by knowledge of theposition of the sun to calculate optimum orientation.

In another embodiment, the solar panels may comprise one or moreparabolic dishes, held within the first or second chambers. The one ormore parabolic dishes are preferably orientated into sun light aroundtwo rotational axes. The one or more parabolic dishes may be made of arestraining ring, which is preferably made of carbon fibre, with mirrorfilm sections that are bonded together to form a parabolic dish. Theshape of the parabolic dish is retained due to the restraining ring. Inthis embodiment, light is reflected by the mirror film and focuses intoa small photovoltaic cell. Ideally, the cell is a triple junction cellwith a Indium Gallium Phosphide (InGaP) junction, Indium Gallium Arsenic(InGaAs) junction and Germanium (Ge) junction on a substrate Germanium(Ge). Cells of this type are available from Emcore Corporation,Albuquerque, USA. Alternatively a four junction cell of GaInNAs,Cu(In,Ga)Se2 Heterojunction cell, or any other photovoltaic solar cellmay be used.

The solar panel may comprise Gold Nano Cups latex substrate that isavailable from Rice University of Texas. This is created using a glasssubstrate and evaporating gold onto nano balls, then applying anelastizer such as latex. When the latex is removed nano plano-concavedlens are formed on the latex substrate (they are all aligned), so thatrandom incidental light, is then made parallel in a single directionafter passing through the latex. Alternatively, latex may be used as a‘former’ and if a resin is applied and the latex ‘former’ removed, nanoplano-convex lens may be present on the resin film (with better opticalqualities). Most light passes through a Photo Voltaic (PV) cell withoutgenerating electrical energy, so use of such a film would bend lightalong the length of the PV film, increasing the path of a photon as itpassed through the PV material. This increases the likelihood of thephoton hitting an electron out of orbit to generate additionalelectrical power. The nano plano-convex film may be added to any PVcell, although it is preferred that the PV cell is on a plasticsubstrate. NanoSolar of the USA has a demonstrated efficiency of 14.6%commercially available on an aluminium substrate. Alternatively, a metalbacked PV film, such as steel, may be used or a polymer substrate.Likewise any PV cell may be employed.

Additional power may be generated in some embodiments by a ThermalElectrical Generator (TEG). A metal foil section is bonded into skin ofthe first and or second compartment or the outer surfaces of the aerialvehicle. Preferably, the metal foil is a TEG metal foil, ideally,bismuth telluride with P-N junctions or any material in the class ofThermal Electrical Generators or alternatively the TEG is attached to ametal foil such as silver, gold, copper or aluminium. Waste heat fromthe solar cells is lost to the interior of the first and/or secondcompartments through convection. The TEG forms part of the chamber (thatis heated through sunlight) and also exposed to colder atmospheric airoutside, the heat differential across the TEG creates electrical energythat may be used to improve overall efficiency of the aerial vehicle. Aheat sink may be attached to the innermost section of the TEG to improvethermal conductivity. Preferably the heat sink is an aluminium honeycombwith high surface area to weight.

In an alternative embodiment, the heat differential between the solarcells (first and/or second compartments) and the external atmosphere maydrive a Sterling or Rankine cycle engine to create additional energythat may either drive the pump directly or a dynamo to produceadditional power. The solar cells may be thermally connected through aheat conductive flexible wire (preferably silver wire or carbonfilament) or flexible heat pipe to the TEG or a metal foil section onthe chamber or outer surfaces (across the Sterling or Rankine engine).

In another embodiment, the aerial vehicle further comprises at least onewing. It is preferred that the wing is substantially flat so itgenerates as little drag as possible. Aerodynamic lift is not requiredto be generated by the wing other than to maintain a glide path, it isinstead provided to assist in generation of a horizontal component fromthe vertical buoyancy driven motion. The wing is a ‘flat plate’ filmwing, with minimal frontal area exposed to the air it penetrates. It ismaintained by a slim symmetrical carbon fibre aerofoil section runningthe length of the wing. A carbon fibre wingtip section maintainsrigidity across the wing. The film may be sandwiched between two carbonfibre parts.

In alternate embodiments the wing may be a substantially symmetricalaerofoil in cross section. In further alternate embodiments the wing maybe an asymmetric aerofoil in cross section. In the case of an asymmetricaerofoil, preferably substantially no aerodynamic lift is generated at azero angle of attack. Preferably, the asymmetric aerofoil may have alift coefficient between approximately −0.01 and 0.01 (based on aplanform reference area)

In embodiments where the wings are a symmetrical aerofoil section, theyare preferably machined of foam with supporting carbon fibre parts alongthe leading and trailing edges and covered with a heat shrunk film (suchas polyester). The ideal thickness of the wing chord is 3.5% of heightto chord length.

In embodiments including a solar panel, the at least one wing maycomprise the solar panel. For example, a flexible solar panel may beinstalled within the wing. In a further embodiment, one or more actuatedparabolic troughs may be installed within the aperture sections of thewing. The parabolic trough is preferably made from mirror film that isheld in place at each end with a parabolic section of carbon fibre thatis actuated to orientate the panel into sunlight. The panels may beactuated individually or together using coupled gears (for example byusing a timing belt).

Depending on the size of the aerial vehicle, the parabolic trough may berelatively small in size. In some embodiments conventional cells wouldbe too large and in that case a solar cell wire may be used at the focalpoint. The wire is preferably made of Germanium with coated layers and acontact for each coated layer. More preferably triple coatings are usedof Indium Gallium Phosphorus (InGaP), Indium Gallium Arsenic (InGaAs)and Germanium (Ge) onto a wire or tube substrate (that may beGermanium). Coatings may be applied by vapour deposition or anyindustrial process that may form a metal coating onto the base material.Any coatings layers and substrates known in the class of photovoltaicsmay also be used. Unlike conventional solar cells, in these embodimentsthe photovoltaic is applied onto a wire or tubular core material, forexample by using a roller to roller manufacturing technique. The tubulararrangement of a solar cell wire has the advantage that a working fluidmay be used to draw heat away from the solar cell. The working fluid maybe used in a sealed heat pipe arrangement to more effectively draw heataway from the solar cell (so it operates at higher thermal efficiency).Preferably a deep parabolic trough is used and the focal point is withinthe trough (or largely in the centre section) where the solar cell wireis positioned, so that light is reflected onto all parts of the wire.

In an alternative embodiment, the PV cell may be incorporated onto thesurface of the vehicle other than on the surface of a wing.

In one embodiment, the nacelle is an aerofoil with a ratio of thicknessto chord length between approximately 5% and approximately 35%. Thisgives a significantly more elongated structure than a conventionalblimp, when the first compartment is incorporated into the nacelle. Ithas been found that this reduces drag, improving performance.

The first compartment has to withstand relatively low pressures,preferably around 0.3 atm. It may therefore be formed from any suitablefilm. However, the time that a vehicle can remain airborne according tothe present invention is limited by the rate at which gas is lost fromthe first compartment, because this will reduce the buoyancy. The filmmay not be effective at preventing the loss of gas through it.Preferably, the wall of the first compartment comprises a barrier layerfor limiting loss of the lighter than air gas through the wall of thecompartment. Examples of suitable barrier layers include EVAL which iscommercially available from Kuraray Co. Ltd. (EVOH), PvdC or PVOH andare encapsulated between a polymer as the barrier is effected by wateringress. HOSTAPHAN® RHBY barrier is commercially available fromMitsubishi (SiOx) and is preferred because its barrier properties areunaffected by moisture and it is also optically clear. The barrier layermay be formed by evaporation onto a substrate in a vacuum chamber, whichmay be manufactured by Alcan of Switzerland, and an additional polymerlaminated to the composite by sputtering adhesive to provide aprotective layer. With such a barrier layer the vehicle may remainairborne for up to 239 days before the lift gas in the first departmentis depleted through loss to the atmosphere, resulting in a 50% loss offree lift.

The second compartment may have to withstand higher pressures than thefirst compartment. There may be a differential pressure of up to 2atmospheres with the outside air. To withstand these pressures thesecond compartment is preferably made from a plastic film which can beultrasonically or radio frequency welded. Examples include AcetalCo/Homopolymer, Acrylic, Acrylic-Impact modified, AcrylonitrileButadiene Styrene, Cellulose Acetate . . . , Polyamide 6 & 66 (Nylon),Polycarbonate, Polycarbonate/Abs, Polyester-Thermoplastic,Polyethylene-Low/High Density, Polyphenylene Oxide, PolyphenyleneSulphide, Polypropylene, Polystyrene-General Purpose, Polystyrene-HighImpact, Polyvinyl Chloride-Flexible, and Styrene Acrylonitrile.

In an alternative embodiment the aerial vehicle further comprises athird compartment for holding a refrigerant which can undergo areversible phase change from a gas into a liquid. The refrigerant may bea refrigerant gas. The third compartment may be located within the firstor second chambers. As the second compartment is filled with atmosphericair (in some embodiments this may also displace the lighter-than-air gasheld within the first chamber), the pressure will increase. The pressurechange may then trigger a phase change in the refrigerant from a gas toa liquid that typically occupies approximately 0.1% of the volume of thegas. This allows the pump of the compressor to work within a loweroverall pressure regime with higher flow rates, allowing more airballast to be accumulated more quickly and improving the aerialvehicle's overall airspeed performance. Iso-butane, butane or otherrefrigeration gas may be used. The total volume of the third compartmentis sufficient to accommodate this gas in its gaseous state, that thethird compartment may be made of a flexible membrane such as latex orneoprene or a polymer film (previously described) that deflates when therefrigerant is in a liquid state. Preferably the refrigerate gascondenses to a liquid state at >1 and <4 ATM absolute pressure at around0° C.

Joints on the second compartment may be reinforced with a glass,plastic, Ultra High Molecular Weight Polyethelene filaments (such asthat sold under the trade name Spectra or Dyneema), or carbon threadsheld in place with resin. The material used for the air ballast chambermay be a composite comprising a matrix held in a plastic laminate. In apreferable embodiment, Spectra or filament is used that may bereinforced with carbon fibres in an encapsulated matrix. This materialis known for use in high performance sail clothing and may be suppliedby Cubic Tech Corporation of Arizona, USA. It is sometimes referred toas Cuben Cloth.

In a further embodiment, the second compartment is a flexible membrane(latex rubber, neoprene or an elastic) or an inflatable chamber (of afilm previously described) held within the first chamber, that mayexpand/contract or inflate to accommodate atmospheric air which ispumped into the second chamber, displacing the lift gas in the firstchamber under pressure. This has the advantage to reduce the overallvolume of the aircraft (reducing drag) and allows the pump of thecompressor to work at a lower overall pressure range across the cycle.Where the first and second compartments share a common membrane or filmto separate them an outer ring of carbon fibre is used to maintain therequired aerodynamic shape of the overall envelope. In an alternativeembodiment the second compartment may be separate from the firstcompartment.

The vehicle may further comprise at least one sensor for aerialreconnaissance or atmospheric monitoring. For example, the vehicle mayinclude ISR sensors such as optical and IR cameras; Synthetic apertureRADAR, for example NanoSAR weighs approximately 900 g and iscommercially available from IMSAR; an acoustic ranging and directionsensor, for example for detecting gunfire, that is commerciallyavailable from ROKE/BAE Systems, Thales or QinetiQ. The vehicle may alsoinclude jamming equipment.

The vehicle may also comprise at least one transmitter and at least onereceiver for providing a wireless communications network. Thetransmitter and receiver could be combined in a transceiver. More thanone transmitter or receiver may be provided to allow communicationaccording to different protocols or for different purposes. In anadvantageous embodiment, a lens can be used to adjust the Field of view(angle) of the transmitter and/or receiver (that can be the parabolicmirror described and the photovoltaic cell may also be the radioreceiver). A standard optical lens, such as is used in a camera, issuitable and the antenna of the transmitter or received is mountedbehind it. This can either provide a narrow field of view to point atanother receiver for point to point networking at very high speed (forexample speeds of 100 Megabits or greater) or provide a wide angle toprovide multipoint to point networking. To give an example, 15 aerialvehicles could provide a Wi-Fi network covering the whole of greaterLondon. In this application modest altitude of around 1 km or highergives line-of-sight between network nodes that are preferably placed ina honeycomb formation. The network may be augmented with surface basedradio repeaters to improve the overall bandwidth across the network.

The at least one transmitter can be used to transmit any form of dataincluding reconnaissance data, meterological data, GPS signals,identification of ocean going vessel and position over AutomatedIdentification System (AIS), radio data and television data.

In embodiments including a solar panel, the at least one receiver maycomprise the solar panel. The solar panel can function effectively as acomponent of the receiver, reducing the overall component count of theaerial vehicle and reducing weight.

The at least one receiver may comprise an antenna formed by a metallisedtrack having an undulating or snake-like pattern. Preferably theundulation is regular, in some embodiments is could be sinusoidal but asquare wave based undulation is preferred. The distance between tracksof undulations is preferably chosen to be a multiple of the radiowavelength desired to be received by the receiver, to improve theantenna performance.

In another embodiment, the control means may comprise a member extendingfrom the rear of the vehicle and an articulated connection between themember and the rear of the vehicle. The articulated connection enablesthe member to be angled relative to the body of vehicle, and preferablyangled to the axis of the nacelle if one is present. The member ispreferably generally cylindrical or rod-like to minimise drag.Surprisingly, such a member can provide a sufficient force to controlthe vehicle. The member may also be configured for rotation relative tothe body, preferably about the axis of the nacelle if one is present.Such a control member can be used to control just yaw, or all of roll,pitch and yaw. A tube or paddle may be added to the end of the member,to increase the deflection into airflow (moment) to orientate thevehicle.

In alternate embodiments pitch may be controlled moving internal massessuch as any batteries or pump that may be present, forward and aft orperpendicular to the main axis to achieve roll control. Rotationalrefinement (yaw) may also be achieved by spinning components, such asthe batteries, if they are provided. Conventional control surfaces, suchas a rudder and ailerons and elevators can also be used in alternateembodiments.

In some embodiments the control means may comprise a movable mass.Control of the pitch of the aerial vehicle may then be achieved bytranslation of the mass from front to back. Roll may be controlled bytranslation of the mass from side to side. Yaw may be controlled byspinning the mass around an axis. Depending on the other control meansprovided, some or all of the control methods using a movable mass may beimplemented.

Embodiments which include a solar panel may form part of an aerialvehicle system which further comprises an electromagnetic radiationsource for emitting electromagnetic radiation for reception by the solarpanel. The electromagnetic radiation source is located remote from theaerial vehicle, for example at a fixed or mobile location on the groundor sea. The electromagnetic radiation may be in the visible spectrum, ormay be outside of the visible spectrum, for example in the range 0.01 to400 nm or 700 to 3000 nm. The electromagnetic radiation source may be acoherent electromagnetic radiation source, such as laser. In someembodiments the electromagnetic radiation source has a focal point whichis the aerial vehicle and the aerial vehicle further comprises means forfocusing incident electromagnetic radiation. The means for defocusingmay be a lens or mirror.

For example, in some embodiments, surfaced based lights may form part ofthe air vehicle system. One or more surfaced based lights may bedirected towards the air vehicle when there is less sunlight available(for example during winter or when in operating at very northerly orsoutherly latitudes). This provides additional power to the solar panelsthan would otherwise be obtained by sunlight alone. Ideally, providingadditional power before dusk. The surface based lights may be actuatedto direct light towards the aerial vehicle, using actuators to orientatethe light beam with two degrees of rotational freedom. The lightsideally use a parabolic reflector or lens to parallelise the light intoa beam or shaft that focuses on the aerial vehicle. The light source maybe a laser. The light may be within the visual wavelength spectrum(400-700 nanometres wavelength) or ideally outside the visual range(200-400 nanometers or 700-2000 nanometres). The surface based lightsmay be at a fixed land position, on a moving surface vehicle (4×4,ground vehicle or ocean going ship) or mounted on a buoy for oceanicoperation. Lighting apparatus for this purposes is commerciallyavailable and actuation is achievable by those in the art. The aerialvehicle may transmits its location to the surface based lights. Forfixed location the surface lighting position is known or, in the case ofa moving surface station, position is obtained by a positioning systemsuch as GPS. The direction from the surface lighting station to theaerial vehicle is calculated and the light orientated towards thisbearing using actuators. The solar panels of the aerial vehicle areorientated downwards to this source of light and additional light energyharvested by the aerial vehicle. This would not be possible withconventional solar powered aircraft that incorporate top facing solarpanels on a fixed wing.

The vehicle may further comprise an electrolyser for electrolysing waterinto hydrogen and oxygen. The electrolyser will produce hydrogen thatmay replace any lighter than air gas lost from the first compartment.The hydrogen may also be used as a fuel. The water for use in theelectrolyser is preferably collected from atmospheric condensation whenair is compressed, water will form in the secondary air ballast chamberand may be pumped to the electrolyser with a micro liquid pump.

In a further embodiment, the vehicle further comprises a jet engine.Excess hydrogen produced by the electrolyser may be stored to power thejet engine. This allows the vehicle to obtain a new position morequickly if required.

Some embodiments may include an outlet at the bottom of the firstcompartment. The outlet may be opened to release any air that is presentin the first compartment as the vehicle ascends. More air will leave viathe outlet than the lighter than air gas because the air is heavier thanthe gas.

According to another aspect of the invention, there is provided a methodof flight for an aerial vehicle comprising a first compartment filledwith a lighter than air gas and a second compartment for holdingatmospheric air, the method comprising:

alternately compressing atmospheric air into the second compartment andthen releasing the compressed atmospheric air from the secondcompartment, thereby altering the buoyancy of the unmanned aerialvehicle such that it is either heavier than air and falling or lighterthan air and rising; and

actuating at least one control means such that the rising and fallingmotion includes a horizontal component.

Unlike the phase change method proposed by Hunt in WO-A-2005/007506, ithas been found that efficient flight can be achieved using compressedair as ballast to alter weight of the vehicle. Controlled flight can bemaintained using a fuel or potentially indefinitely with an externalenergy source, such as solar power.

Embodiments of the invention will now be described with reference to theaccompanying drawings in which:

FIG. 1 is a perspective view of a diagrammatic representation of anaerial vehicle according the present invention.

FIG. 1A is a detail of a leading edge wing arrangement of FIG. 1.

FIG. 1B is a detail of a mid section wing arrangement of FIG. 1.

FIG. 1C is a detail of a trailing edge wing arrangement of FIG. 1.

FIG. 1D is a detail of a Thermal Electrical Generator foil insert thatmay be used with the embodiment of FIG. 1.

FIG. 2 is a cross section and end view of a solar cell arrangement foruse with the invention.

FIGS. 3A and 3B depict a diagrammatic representation of a reinforcingarrangement for use with the vehicle of FIG. 1.

FIGS. 4A and 4B depict a diagrammatic representation of an alternateballast compartment for use with the vehicle of FIG. 1.

FIGS. 4C and 4D depict cross sections through the ballast compartmentsthat can be used in the vehicle of FIG. 1.

FIG. 5 depicts a diagrammatic representation of an optional thirdcompartment inserted with the ballast compartment.

FIGS. 6A, 6B, 6C and 6D are a plan views of a diagrammaticrepresentation of embodiments of a wing with an integrated aerial foruse with the vehicle of FIG. 1.

FIGS. 7A, 7B and 7C depict a diagrammatic representation of a crosssection through a solar cell for use with the vehicle of FIG. 1.

FIG. 8A, 8B, 8C and 8D depict a diagrammatic representation of annegative refraction index film for use with the vehicle of FIG. 1.

FIGS. 9A and 9B depicts a cross section through a film for use with acompartment of the vehicle of FIG. 1.

FIGS. 10A, 10B and 10C depict alternative embodiments of controlsurfaces that may be used with the vehicle of FIG. 1.

FIG. 10D depicts a diagrammatic representation of a symmetrical wing asan alternative embodiment. FIG. 10E depicts a cross section of asymmetrical wing.

FIG. 10F depicts an alternative embodiment of a parabolic solar troughwithin the symmetrical wing.

FIGS. 11A, 11B and 11C depict alternative profiles for the body of theaerial vehicle of FIG. 1. FIG. 11D depicts a diagrammatic representationof a blended fuselage and wing configuration.

FIGS. 12A, 12 b, 12C, 12D, 12E and 12F depict plan views of the wingprofiles that may be used in various embodiments of the invention.

FIG. 13 depicts an optional wing tip nacelle that may be used with thevehicle of FIG. 1.

FIG. 14 is a conceptual diagram showing the arrangement of controlsystems, payload and communication systems within the vehicle of FIG. 1.

FIGS. 15A and 15B are a conceptual diagrams depicting an alternativeembodiment of the vehicle. FIG. 15A is a conceptual diagram of alighting unit for use with FIG. 1 of the vehicle.

FIGS. 15C, 15E and 15G are conceptual diagrams of alternativeembodiments of the parabolic solar harvesting apparatus.

FIGS. 15D, 15F and 15H are cross sections of alternative embodiments ofparabolic mirrors.

FIG. 16 is a diagrammatic representation of an aerial vehicle accordingto a further embodiment of the invention.

FIGS. 16A and 16B depict cross sections through the solar cellarrangement and body section of the vehicle of FIG. 16, respectively.

FIGS. 17 and 17A is a diagrammatic representation of an aerial vehicleaccording to another embodiment of the invention.

FIG. 18 is a diagrammatic representation of an aerial vehicle accordingto a further embodiment of the invention.

FIG. 19 is a conceptual diagram illustrating the method of flight of thepresent invention.

FIG. 20 is a graph showing freelift and ground speed versus altitude fordifferent angles of ascent.

FIG. 21 is a graph showing ballast and ground speed at various glidingdescent angles.

FIG. 22 depicts an equilibrium gliding descent.

FIG. 23 depicts an equilibrium gliding ascent.

FIG. 24 is a graph of lift and drag coefficients with angle of attack.

FIG. 25 depicts a mesh network application.

FIG. 1 is a diagrammatic representation of a perspective view of a firstembodiment of the present invention. The first embodiment is an aerialvehicle, considering the vehicle from it's rear to it's front, itcomprises a rudder 1 actuated by a servo 2. The rudder preferablycomprises carbon fibre sheet with an aperture to reduce weight. Film isdraped over frame and attached to the frame so that the film is taut.The rudder 1 comprises two parts: top and bottom. The top and bottomparts are attached with a rod. The rod forms the pivot point and isactuated with the servo 2. The pivot point is preferably placed at thecentre of pressure so the arrangement is easy to turn with a very smallservo.

The rear of the vehicle also comprises a stabiliser 3. Preferably, thestabilisers 3 are static. However, in alternative embodiments, they maybe actuated to function as elevators. In that case the area 4 markedwith a dashed line may be removed to allow them to move and avoidinterference with the rudder.

The rear section of the vehicle, supporting the rudder 1 and stabiliser3, comprises a cone 5. It is preferably a carbon fibre cone with a cap.The cone houses a processor to function as the autopilot and theautopilot sensors (discussed in more detail below). An envelope film 13interfaces with the cone and is held in place with resin andglass/carbon fibre fabric reinforcement.

Moving forward from the cone 5, the vehicle comprises a rear ballastchamber or compartment 6. This is made from either plastic film orreinforced film. Preferably, a plastic film sandwich is used comprisingUltra high molecular weight polyethylene (UHMWP) or UHMWP filaments(such as those sold under the trade names Spectra or Dyneema). If afilament is used, it is not woven as this would allow stretch,potentially altering the external surface shape of the compartment.Alternatively, other thread materials may be added to form a matrix(e.g. glass or carbon fibre) and may be layered in differentorientations for strength in more than one direction.

Extending into the rear ballast compartment are strengthening sections7. These are provides to maintain the shape of the interface with theadjacent compartment 13 when the rear compartment 6 is under pressure.The strengthening sections 7 may be a UHMWP composite. A divider 8maintains separation between the rear ballast compartment 7 and theadjacent compartment 13. It may also be formed of a carbon or UHMWPcomposite.

The adjacent compartment is defined by envelope film 13 and is filledwith a lighter than air gas to provide lift to the vehicle. Within theenvelope is contained a servo 9 to rotate a solar cell arrangement suchthat the solar cell arrangement is preferably oriented towards the sun.Electrical power can be transferred to the servo through a slip ring andcarbon brushes on the servo connection shaft.

The solar cell arrangement can also be seen in cross section in FIG. 2.It comprises an end frame 10, a parabolic strip 18, a half-pipe lengthcomprising horizontal section 15 and vertical section 16 and a solarfilm mount/servo connector 17. The parabolic strip 18 may be draped overthe required profile under heat. The horizontal section 15 and verticalsection 16 are preferably carbon fibre. The solar cell arrangement alsocomprises mirror film 11. The solar film mount/servo connector 17 isalso made from carbon fibre and allows a solar film 12 (at the bottom)and mirror film (at the top) to be mounted at each end. It also providesa mounting for the servo which connects the trough to the body. Themirror film 11 is ideally made of plastic with high optical qualities(such as acrylic) and metalised. Silver is evaporated onto the film inthe preferred embodiment with a protective coating (of Silicon orAluminium to reduce oxidisation) or laminated layer (such as acrylic).Alternatively aluminium, platinum, gold or another metal that is highlyreflective and ideally inert may be used to metalise the mirror film 11.Thin Solar film 12 is formed around a mounting section. A metalised filmruns across the top section. The mirror film 11 reflects sunlight andreduces heat build-up on the rear of the solar film 12 and helpsmaintain the profile of the solar film 12 across its length.

In the preferred embodiment a copper indium gallium diselenidephotovoltaic (PV) panel is used on an aluminium foil back plate (astainless steel foil or polymer backplate may also be used). NanoSolarof San Jose, US manufacture such a film and has an independentlyverified efficiency of 14.6% (NREL). A gold nanoball film (or derivativeof this process) may be added onto of the cell (detailed separately).Any PV thin film may be used including: amorphous silicon (a-Si), copperindium diselenide (CuInSe₂, or “CIS”), cadmium telluride (CdTe).Additionally a thin triple matched junction PV cell may be used,available from Spectralabs (Boeing), Sylmar, Calif., USA with anefficiency of over 40.7% under 240 suns or a Inverted MetamorphicMultijunction (IMM) Solar Cell available from Emcore Corp ofAlbuquerque, N.M. with an efficiency of 40.6% under 326 suns. Such cellsmay be mounted on both sides of a substrate, for example an aluminium ortitanium plate, to form a panel that is mounted vertically.

It should be noted that the focal point for the mirror film 11 is notobvious. Light is bent as it moves through materials of differentdensity. For example as it moved from air to hydrogen, there will be aslight bending inwards of light. In an embodiment in which envelope 13is filled with Hydrogen, the focal point may be optimised fordiffraction through the hydrogen. Likewise, the focal point may beoptimised for whichever lighter than air gas is used within the envelope13.

The envelope 13 defines a compartment for lift gas. It is made from atransparent barrier film, that is ideally cut into panels (for exampleby waterjet CNC or cutting plotter), and then ultrasonically or RFwelded. Alternatively, it may be thermally bonded or joined with anadhesive. Weldable materials are preferred, including AcetalCo/Homopolymer, Acrylic, Acrylic-Impact modified, AcrylonitrileButadiene Styrene, Cellulose Acetate . . . , Polyamide 6 & 66 (Nylon),Polycarbonate, Polycarbonate/Abs, Polyester-Thermoplastic,Polyethylene-Low/High Density, Polyphenylene Oxide, PolyphenyleneSulphide, Polypropylene, Polystyrene-General Purpose, Polystyrene-HighImpact, Polyvinyl Chloride-Flexible, and Styrene Acrylonitrile.

Resins may also be applied to seams and glass/spectra/carbon clothreinforced to provide a strong joint. The envelope 13 is preferablyconstructed as a sandwich to incorporate a gas barrier component,normally an adhesive is used to bond the film laminated parts together.Suitable barriers include PvdC, EVOH (EVAL) or PVOH. A typical layer forthis purpose will be around 10 μm sandwiched between a 15 μm plasticfilm (25 μm total). A more preferable alternative is a ceramic barrierthat is vacuum evaporated onto a substrate film, SiOx or AlOx, forexample that is sold under the trade name Hostaphan. A thin protectedfilm is normally laminated to the ceramic barrier layer. A combinationof sandwich films may be applied.

Continuing to move towards the front of the vehicle, a front ballastchamber or compartment 14 is provided with construction as describedabove for the rear ballast compartment 6.

The operation of the solar cell arrangement is indicated on FIG. 2.Incident light (indicated by arrow 19) is reflected (indicated by arrow20) from the mirror film 11 towards the solar film 12 and the solarcell.

Extending from opposite sides of the vehicle is a wing 21. This may bemade of any bondable material and may be metalised to reflect furtherlight towards the solar cell arrangement. The leading edge 22 is shownin more detail as a cross section in FIG. 1A. The film is wrapped arounda carbon fibre strip and bonded to itself. The mid section is shown inmore detail in the cross section of FIG. 1B. Two carbon fibre sectionsare bonded to the wing 21 to form a symmetrical aerofoil. This is a lowprofile aerodynamic structure with little bending. Supports between theleading and training edge may be provided. The trailing edge 24 is shownin more detail in FIG. 1C, the construction is the same as for theleading edge 22. The wing 21 is supported by ring 25 which is connectedto struts 26. The ring 25 may be internal or external to the envelope13. A Thermal Electrical Generator (TEG) Foil insert 13 a is position inthe chamber 13 as shown in FIG. 1D. A heat sink 13 b thermally conductsheat away from the chamber to the TEG 13 a, that is cooled on itsatmospheric air facing side.

Located within the envelope 13 is a payload 29. A tether wire 28,preferably a UHMWP filament, extends from the payload 29 to tetheranchor points 27. The payload 29 contains an actuator, such as a winchservo, which can pull the payload along the main axis of the vehicle forpitch control. The wire 28 may be kept in tension by a spring.

The payload 29 typically comprises: batteries, battery heater, pumps,valves, servo. This is typically a foam container that incorporates thecomponents with an aperture to allow for the movement of actuatedmovable masses (such as batteries in one embodiment). Electroniccomponents that generate electro-magnetic fields may be shielded in a Mumetal foil that may also draw heat away from the component to theoutside of the container (this may reduce interference to any sensors,such as the autopilot). For example permalloys containing approximately80% Nickel (Ni), 20% Iron (Fe) and small amounts of Molybdenum (Mo). Anickel-iron-molybdenum alloy (permalloy) which offers extremely highinitial permeability and maximum permeability with minimum hysteresisloss. The foam container is encapsulated in a plastic film.

The battery 30 may slide along the secondary axis to achieve rollcontrol with an actuator that may be a servo with sliding gear or winch.In some embodiments, the battery may be rotated at speed for control ofyaw. The battery 30 is preferably Lithium Sulphur with a specific energyexceeding 260 Wh/kg (commercially available from Sion Power). Carbonnano tube structures may be used as the electrodes to improve the totalsurface area so more power can be pulled from the cell. Otherrechargeable technologies may also be used such as Lithium Polymer andLithium Ion if larger number of charge cycles are required beforereplacement, or any other suitable technology, such as lithium airbattery cells. A high energy density is preferred to reduce the weightof the vehicle.

FIGS. 3A and 3B is a perspective view of a reinforcing arrangement thatmay be used for the envelope 13. It depicts only those parts of theaerial vehicle relevant the reinforcement. It comprises a receivingsleeve 32 for receiving a reinforcing rib 33. The sleeve may be weldedto the envelope 13. The reinforcing rib 33 is preferably made of carbonfibre. Further support is provided by O ring 34. The reinforcement isoptional. Alternate embodiments may include addition reinforcement, forexample more O rings 34.

FIGS. 4A and 4B depict an alternative constructions for the ballastchamber or compartment 35. Optional film sections 38 may hold the secondcompartment in position and form a void within the second compartment35. This has the advantage compared with a film envelope which may becrushed. The ballast chamber is held in tension to maintain a shape(void), so that the chamber does not need to be pre-inflated before airballast can be accumulated, saving energy and increasing performance.The void is a ideally a bi-pyramid. Preferably an eight sided bi-pyramidis used as shown in FIG. 4D (cross section) and isolation from theenvelope 13. In other embodiments the bi-pyramid may have more or fewersides than eight as illustrated by FIG. 4C. These are contained withinthe outer structure for reduced drag. FIG. 5 shows an optional thirdcompartment 37 in isolation. The third compartment is filled with arefrigerant gas that when in a gaseous state may occupy the void in thesecond compartment 35. When the second compartment is pressurised, therefrigerant gas changes to a liquid state (occupying approximately1000^(th) of the volume and allows the pump to work in a lowerdifferential pressure regime with higher flow over the compressioncycle. The third compartment may be positioned in the first compartmentor the second compartment or between the first and second compartment(not shown).

An exemplary wing film structure used in alternative embodiment isdepicted in diagrammatic form in FIG. 6A. The wing structure comprisesan aerial 40 a, which is a circuit pathway onto a film substrate, foruse with a transmitter and/or a receiver. A metalised coating may beapplied to the film by splutter vapour disposition. The film may bemetalised by the deposition of ideally silver, aluminium or gold or anymaterial that can be applied using this method. The circuit pathways areshown for illustrative purposes only and are not to scale. In thepreferred embodiment the distance between pathways is a multiple of theradio wavelength of interest. FIG. 6B shows the preferred embodimentthat uses a repeatable pattern 40 b, that is applied in the metalisationof polymer films, using a roller to roller manufacturing technique.Unwanted parts of the circuit pathway can be removed by acid etching(for example, as used in circuit board production) and circuit pathwayscreated with a silver impregnated ink 40 c, protected with a resin topcoat to isolate the circuit from the elements. FIG. 6C shows therepeated pattern in isolation. FIG. 6D shows an alternative embodiment,with the repeated circuit pattern 40 d. Additional circuit pathways 40 eare provided in this repeatable pattern that can be used toindependently connect other electronic devices or antenna circuits. Thistechnique can be applied to any film parts of the airframe, allowing theentire airframe structure to become a radio antenna. Additionally thistechnique may be applied to sections, such as the wingtips to create anindependent antenna that can be used, for example, for a SyntheticAperture Radar antenna, with a wide distance between stereo antenna.

FIGS. 7A, 7B and 7C depict diagrammatic representations of a solar cellfor use in the present invention. A Photovoltaic solar cell is depictedat 41. A transparent nano plano-convex polymer film 42 is provided ontop of the solar cell 41 in FIG. 7A. Light is bent along the length ofthe film, so increasing the length of its passage through the PVmaterial, giving a photon a better chance of hitting an electron out oforbit (indicated by arrows 43, showing photon paths). FIG. 7B depicts atransparent nano plano-concaved polymer film 44. FIG. 7C depicts theshorter path length when a nano plano-convex or nano plano-concave film42 or 44 is not used.

FIG. 8A, 8B, 8C, 8D depicts an alternative embodiment of films with anegative reflective index used on the wings and chambers. A transparentnano plano-convex polymer film 42, is optically bonded to a clear film(typically of higher density) 45. Light is bent as it passes through theplano-convex film 42 and enters the second film 45 of typically higherdensity and bounces between this film in the same way as light travelsdown an optical glass fibre filament, until it hits the PV cell at theend of film 41. FIGS. 8B and 8D shows the passage of light through aplano-concaved polymer film 44. FIGS. 8C and 8D show the application ofa triple junction coated photovoltaic wire installed within a polymerfilm. These configurations represent very light weight, very highefficiency solar panels that may be installed into the aerial vehicle.Additionally, the PV cell may be utilised as an antenna to receive radiowavelengths of interest.

FIG. 8 depicts a cross section (side view) through the film that may beused for the first, second or third compartments. The film comprises twobase layers components 46, sandwiched between a bonding component thatmay be a gas barrier such as EVOH (trade name EVAL), PVOH or PvdC andmay also comprise further unidirectional reinforcement filaments 48(running in the x axis) and 49 running in the y axis, of carbon, glass,UHMWP or any reinforcement filament in the class of reinforced plasticcomposites may be employed. Additional layers of reinforcement may alsobe used, e.g. triaxially orientated with the filaments aligned at 60°,120° and 180° for strength and/or flexibility. A plastic film 46(preferably an ultrasonically or radio frequency weldable plasticmaterial) forms a base layer. It has a thickness preferably from 2 to 80μm. An adhesive layer 47 bonds plastic film 46 to a first barriercomponent 48. The adhesive is also a gas barrier component 47 such asPvdC, EVOH (EVAL) or PVOH at a thickness of 2 to 20 μm. A secondary gasbarrier component 46 b is evaporated onto the first base film that alsoprovides a gas barrier. A second gas barrier component 46 b is a ceramicbarrier that is vacuum evaporated onto a substrate base film of SiliconOxide or Aluminium Oxide or other gas barrier that may be applied withthis method with a typical thickness of 1 μm. A further layer ofadhesive 47 and plastic film 46 are then added to complete the compositesandwich film. In other embodiments the barrier layers may not be used,or only one layer used. However, two layers are preferred to limit lossof lift gas from compartment 13. FIG. 9 depicts a cross section (endview) through the composite sandwich film.

FIGS. 10A, 10B and 10C depict alternative embodiments of control andstabilising surfaces that may be used with the present invention. In theembodiment of FIG. 10A, a pole or generally cylindrical member 54extends to the rear of the vehicle. The pole may be tapered and in someembodiments has a paddle or additional control surface appendage (notshown), The member 54 is articulated or pivoted where it extends fromthe rear of the vehicle. An actuator 55 may move the pole up and downusing a linear actuator, such as a servo driving a threaded bar with aretaining screw within the member 54. The whole arrangement may also berotated and pivoted 56. This allows the member to point in any givendirection and achieve yaw, pitch and roll control with minimal drag whennot in use. An alternative embodiment in FIG. 10B uses a split rudder57, 58. It is preferable that the pivot is at the centre of pressure ofthe stabilising/control surface (e.g. the quarter chord point from theleading edge), so a smaller actuator can be used. Alternatively,conventional fixed stabilisers with a separate actuatedrudder(s)/elevators positioned at the trailing edge. The embodiment inFIG. 10C uses a rudder 59 with elevators 60, 61.

FIG. 10D shows an alternative embodiment of a wing, using a symmetricalaerofoil section. Ideally made from a foam core 23 b with sectionsremoved to reduce weight. A reinforced carbon fibre or compositereinforced leading edge member 22 b and trailing edge member 24 b. APhotovoltaic solar panel that is ideally a flexible film that may beimplemented over the entire wing surface (top and bottom). A clear heatshrunk film is applied 41 b, such as polyester, over the foam core 23 b.An optional composite aileron 21 c, that is actuated to achieve rollcontrol. A composite wingtip plate member 21 d may be attached to thefoam core 23 b. The wingtip plate reduces vortex induced drag on thewing by providing a fence, so that air cannot roll away from the wing atthe wingtip. Unlike a conventional winglet, the fence reduces vortexinduced drag on gliding accent and descent. In some embodiments acomposite tube member 41 c may extent through the main chamber(fuselage) and extend proud of main chamber—not shown and provide amounting for the wings. The foam core 23 b has a receiving aperture (notshown) and wing slide over tube member and attach to the main chamberwith a fixture.

FIG. 10F is an alternative embodiment of the wing previously describedin FIG. 10E, that instead, uses parabolic mirror film 21 e, to reflectlight into a small photovoltaic cell 21 f, under concentration. Ideallythe PV cell 21 f is a triple junction wire type, described herein, butmay be any cell known as a photovoltaic cell. The parabolic trough maybe orientated by a servo (not shown). One or more parabolic troughs maybe orientated together by a timing belt 21 h using a toothed gear 21 g.In alternative embodiments, a simple gear arrangement may be used or thetroughs may be orientated individually using separate actuators (notshown).

FIGS. 11A, 11B and 11C depict alternative profiles for the body of theaerial vehicle (excluding wing). FIG. 11A is the most preferred profile.It depicts an axi-symmetrical aerofoil body of revolution. Theembodiment of FIG. 11B is an axi-symmetrical Vescia Piscis body ofrevolution. FIG. 11C depicts a further embodiment which has anasymmetric aerofoil. This may generate conventional lift (top) or beflipped over to generate negative lift (bottom). Surprisingly, in theembodiment of FIG. 11C, better performance can be obtained if theaerofoil is arranged to generate negative lift in gliding ascent(illustrated in the lower part of FIG. 11C), when energy consumption isconsidered. More energy is generally available when the vehicle isascending due to buoyancy so the aerofoil can have most effect with thisorientation. FIG. 11D, illustrates how more than one compartment 64 canbe implemented to create a morphed fuselage/wing. A dotted line 65represents a skin around the compartments. The profiles in FIGS. 11A,11B and 11C apply to the main body or nacelle of the vehicle.

FIGS. 12A, 12B, 12C 12D, 12E, 12F and 12G depict plan view of the wingprofiles that may be used in various embodiments. For clarity these areshown with the body profile of FIG. 11A, although any other body profilemay also be used. Next to FIGS. 12A, 12B 12C, 12D, 12E, 12F and 12G areshown diagrammatic representations of the different vertical positions(in side view) relative to the body where the wing can be mounted and tothe right of this (in front view). For each is shown a top wing, midwing (preferred) and bottom wing respectively. FIG. 12A shows a taperedwing embodiment. FIG. 12 B shows a straight wing embodiment. FIG. 12Cshows a swept wing embodiment. FIG. 12D shows a delta wing embodiment.FIG. 12E shows an elliptical wing embodiment. FIG. 12F shows a canardwing embodiment. For clarity, this can be a plurality of pairs of wingsof any planform, size, type or position In all these embodiments it ispreferred that the wing generates minimal lift and is substantially flator symmetrical to maintain a gliding path, preferably with an angle ofattack of ±0.5°. In other embodiments the wing may generate a smallamount of lift or have a more pronounced aerofoil profile.

FIG. 13 depicts an optional wing tip nacelle 80 that may be provided ifextra lift is required. The nacelle 80 forms a further compartment forlift gas or ballast with a construction as described above for thecompartments. FIG. 13 represents one or more additional compartmentsthat may be added to the wing, ideally this is at the wingtip.

In a preferred embodiment, for use as an unmanned aerial vehicle, themain nacelle has a body length of 6.8 m and a thickness of 15% of chordlength. It will be appreciated that dimensions and chord thickness maybe varied depending on the particular application and payload for thevehicle.

FIG. 14 is a conceptual diagram showing the arrangement of controlsystems and payload within the vehicle. One or more solar cells 201generates electrical power from incident light. The solar cell 201 isconnected through a corrective diode 202 to a battery 203. The diode 202ensures that power is not drawn from the battery 203 by the solar cell201 at night. The battery may be Lithium Sulphur supplied by Sion Powerwith a specific energy of 260 Wh/kg or a lithium Polymer cell(approximately 200 Wh/kg). Carbon nano tubes may be used at theelectrodes of the battery 203. Power from the battery 203 is used forthe control and electrical systems of the vehicle. In the preferredembodiment a Lithium Air battery is used, experimental cells areavailable from St Andrews University, Scotland, UK, the theoreticalspecific energy is as high as 2 kWh/kg.

Block 208 illustrates a positioning system. Various positioning systemsthat may be included in the invention. One or more of the systems may beincluded, including more than one system allows redundancy. GPS system204 may provide XYZ position, 3 axis bearing and speed taken at asampling rate of 0.25 Hz to 1 Hz with current technology. Alternately apositioning device 205 adhering to the Long Range Navigation System(LORAN) or LORAN-C standard may be provided. A positioning device 206adhering to the SHOrt RAnge Navigation System (SHORAN) may also beprovided. Another positioning device 207 uses a plurality of eitherfixed and known transmission stations with an embedded time code of timeof transmission. Any transmission station transmitting a radio signal onany bandwidth which embeds its position and time of transmission may beused. The transmission station may be a surface station.

The vehicle may remain airborne for several days or longer and cantherefore assume many of the roles of a satellite, includingtransmitting a GPS, LORAN-C or SHORAN signal, providing pseudo-satellitefunctionality.

In an alternate embodiment the vehicle may identify fixed landmarks toestablish its own position and then transmit its position andtransmitted time code to allow GPS or other navigational system devicesto operate, should other GPS or other services be denied. A plurality ofaerial vehicles can transmit a position with embedded time code usingthe appropriate standard to receivers in the area, restoringnavigational services. This has the advantage that the signal strengthis much stronger compared with a satellite transmission andsignificantly more difficult to disrupt.

Block 217 illustrates sensor inputs that may be provided. The vehiclemay include one or more of:

-   -   a three axis accelerometer 218;    -   a three axis infrared sensor 219, which may be used to determine        orientation. The sensors point in all directions and the        airframe orientation relative to the warm earth and cold sky can        be deduced by the relative IR measured.    -   a three axis electronic compass 220;    -   a light meter 221    -   a Hydrometer/humidity sensor 222;    -   a temperature sensor 223;    -   a pressure sensor 224;    -   a rotary encoder 225 to establish the rotary position of a        motor;    -   a Power meter 226, to monitor the status of the battery.

One or more transmitter/receivers are also provided. For example a lenscorrected radio transmitter receiver/transmitter 227. This may focus asignal specifically at a target. For example, it may direct a signaldirectly at another vehicle for high speed point to point networking orto pickup a weak signal from a specific ground transmitter. Thetransmitter may be mounted with one or more of the parabolic mirrorsdescribed and actuated towards the mirror to change its focal length.One or more transmitter or receiver 228 may integrated into the film ofthe wings, for example using an aerial 40 as discussed above. Aunidirectional transmitter or receiver 229 may also be provided.

An autopilot 209 receives inputs from the positioning system(s) 208, thesensors 217 and the transmitters and receivers 227,228,229. These inputsmay be analogue or digital. The autopilot is typically implemented in amicroprocessor, ASIC, system-on-chip or any other system that canreceive and process information. It generates an output to control thevehicle. The functions of the autopilot are illustrated in graphicalform on FIG. 14.

The autopilot 209 is configured to determine 210 an XYZ position andorientation in space. This is done by calculating an expected speed andfuture position based on a predetermined aerodynamic model and adjustingthese with actual data from the sensors. For example, the sensors mayreveal wind speed and direction, which may be stored in theMeteorological database (described below) with time stamp. The autopilot209 may plot a route to a loitering position that may include waypointsby referencing the Meteorological database. The auto pilot may alsoreceive a target position, used to co-ordinate camera and sensor gimbalsto look at a target position from its current position.

The autopilot 209 includes an accurate clock 211. Input data may be timestamped. The autopilot 209 also preferably includes storage means suchas random access memory, which may be non-volatile such as a flashmemory. This storage means can be loaded with various database such as a3D map 212 of terrain, country boundaries and segregated air space type.Building geometry and other objects of interest may also be included.The autopilot 209 may reference this 3D map to ensure it is not going tocollide with any objects or terrain. It may also be used for determiningright of passage through airspace.

A meteorological database 213 may also be included. This may comprisedata on: wind speed and direction at various altitudes, humidity,sunlight intensity, pressure, chemical composition of air or othermeteorological conditions. The meteorological data may be shared withother vehicles and receiving stations. The vehicle may receive met datafrom external sources for route planning Reports may be transmitted viaAIREP (Aircraft Report), encoded according to the AFMAN manual 15-124pages 32-35 or any other accepted Meteorological data reportingstandards.

An object of interest database 214 may be included. These may include:other aircraft in the vicinity, ships or vehicles. Ships position aretransmitted using the AIS system Automatic Identification System and arerequired on all ships with a gross weight over 300 tons. The sensors mayidentify small vessels not equipped with AIS and broadcast thesepositions across the AIS network. This could be particularlyadvantageous if the vehicle is used for monitoring by the coast guard.

Aircraft typically transmit their digital position using ACARS (AircraftCommunications Addressing and Reporting System), ADS-B and HFDLstandards which could be included in object of interest database 214.Both known positions and sensor feeds may be used to plot a course toavoid airborne objects and aircraft, providing ‘sense and avoid’.

A datafeed database 215 may also be provided for storing informationfrom sensors. In addition to the inputs described above, sensor feeds250-257 (discussed in more detail below) may be stored in the datafeeddatabase 215 with an associated geocode for the position of the feedwith an embedded time stamp. Many feeds may be compared from differentangles to reveal geometric shapes. The raster information relating to ageometric shaped may be extracted, perceptively corrected and mappedonto the surface of the shape or face within a 3d model. Many feeds maybe compared, where the raster information is persistent or similar, thisdenotes a permanent object. Where a higher resolution source isavailable the resolution of the base map may be improved. Many sourcesmay be used to composite a 3d model of terrain and permanent objects(buildings and structures). A feed may be compared with the 3d modelwith mapped surfaces that may be adjusted to compensate for the sun'sposition and intensity as it hits a face in the 3d model and transitoryobjects identified as they appear on the base map, which may be passedto the objects of interest database. This database 215 may also bestored externally and updated by the Aerial Vehicle. A subset of the 3dmap and related raster information relating to current operating areamay be extracted from a central external database and stored in thisdatabase.

Another database, setting database 216, may also be provided. Thisincludes the current setting of the vehicle, for example the position ofservos.

The autopilot 209 may also include a watchdog system for checking thehealth of the autopilot and taking remedial action, such as restartingit if necessary. Two or more autopilots may be used in alternateembodiments for redundancy.

The autopilot 209 is connected to various actuators for controlling thevehicle. These include optional Mass positioning servos 234, Controlsurface servos 235, optional Gyroscope motor 237 (which may be threeaxis) for maintaining a stable platform for sensors, optional mirroractuators 238, for stabilising a camera image, optional Gimbal servos239 which may be three axis to orientate sensors, optional Lens cameraservos 240, valves 241, parabolic mirror/solar cell actuators 233 b,transmitter/antenna actuation that may include controlling the focallength (not shown), Pump 242, optional Water reservoir 243 (water willaccumulate as atmospheric air is compressed and collects in the waterreservoir 243. The water may be purged or converted to hydrogen toreplace lost lift gas through electrolysis), optional electrolysis unit246 containing water with anode 244 producing oxygen (typically expelled231 d) and cathode 245 producing hydrogen.

Optional Lamp 233 (a red lamp is presented on the left (port) side, agreen lamp is presented on the right (starboard) side, a white strobelight is positioned at top and bottom extremes of the airframe),optional LED 247 with a colour scheme as above. The lamps/leds 233, 247may be within the wingtip section. This would provide sufficientluminosity to meet CAA requirements with little additional drag,optional Electrical heater 248 for heating a battery so power can bedrawn in cold operating conditions or heating a refrigerant gas held inthe third compartment to change from a liquid state to a gaseous state.A refrigeration unit (not shown) for cooling a refrigerant gas from agaseous to its liquid state.

An optional Shielding 249, which is a magnetically shielding metal or Mumetal foil, may surround the components of the electrical system.

The pump 242 is preferably a Diaphragm pump. Any suitable pump forcompressing air may be used in alternative embodiments, such as scroll,vane, reciprocating, piston, rotary screw, diagonal, axial flow andcentrifugal pumps. A micro pump 242 b may be used to pump hydrogen intothe main compartment (that may be partitioned in it's own chamber). Thefirst compartment may have an additional chamber 231 c that isindependent filled with a lighter than air gas, should control orcommunications be lost a valve opened, to vent the lighter then air gasto the atmosphere 231 d and reduce overall buoyancy to force a slowdescent.

Further actuators may be included for the alternative embodimentincluding a drogue (described in more detail below with reference toFIG. 17). These include a solenoid 232 for deploying the drogue and awinch servo 236.

Depending on the application of the vehicle, various sensors may also beincluded. These include an optical camera 250, that may be colour orgreyscale, CCD, CMOS or line scan. The camera 250 may be gimbalised andstabilised with gyroscope or mirror gyro, with or without a zoom lens.Providing more than one camera 250 spaced apart allows a range to targetobject to be determined.

An Infrared camera 251 may be provided, that may be colour or greyscale,CCD, CMOS or line scan. That IR camera 250 may also be gimbalised andstabilised with a gyroscope or the image stabilised with a mirror gyro,with or without a zoom lens. Spacing two IR cameras apart focusing on asingle object allows a range to be established.

One or more microphones 252 may be included. Preferably a number ofacoustic sensors are mounted spaced apart to establish a direction anddistance to a source of sound. Microphones are preferably mounted at thewing tips and front and aft of the vehicle. The sensors' timing may becompared to establish the direction. This may be referenced against a 3dmap to establish a point of origin for the source of the sound.

A RAdio Detection And Ranging sensor 253 may be included. Suitable typesinclude: Monopulse radar, Bistatic radar, Doppler radar, Continuous-waveradar or Synthetic Aperture RADAR (SAR—e.g. A nanoSAR supplied by IMSARor PicoSAR from Selex). Operating ranges may include the HF to UWBranges, passive or active. The RADAR sensor may be placed at the focalpoint for the parabolic trough used for the solar cell.

A Light Detection and Ranging sensor 254 may be included. Suitable typesinclude: Elastic backscatter LIDAR, Differential Absorption LIDAR(DIAL), Raman LIDAR, Doppler LIDAR, Synthetic Array HeterodyneDetection. A Laser Detection and Ranging module 255 may also be used.The LIDAR sensor may be positioned at the focal point of the parabolictrough used for the solar cell.

A Sound navigation and ranging (SONAR) sensor 256 may also be included.This can be Active (infrasonic to ultrasonic range) or passive orSynethic aperture sonar, such as a Vision 600 SAS manufactured byQinetiQ, UK. The sensor may be placed at the bottom of the airframe. Thevehicle may land on a body of water to take a reading. Preferably thesonar is independent of the airframe and carried as a payload, within abuoy, the aerial vehicle may drop the payload at the sampling site andrecover it using a skyhook or Fulton type surface to air recoverysystem.

A SODAR (SOnic Detection And Ranging) sensor 257 may also be included.This is for met measurement of wind. A transducer is placed in the solartrough that bounces sound into the atmosphere and returns a sonic signalto the microphones.

The sensor payload may include a projective laser spectroscopy sensor(not shown) currently being developed by St Andrews University,Scotland. This sensor can be used to sample air for chemicals ofinterest (detecting less than one part in a million). The sensor caneither take samples from the air ballast chamber or air that passes overthe airframe and in due course may have sufficient range to penetrate toa surface target of interest to establish its chemical composition.

The iconography at the bottom of FIG. 14 showing communication of thevehicle with other equipment. A ground station 258, may allow manyvehicles to be controlled and/or coordinated. The ground station 258 mayreceive the current state of the vehicle settings, receive databases orsubsets of the data (212-216), provide new target co-ordinates andwaypoints and specify target imaging locations for sensors. Intelligencesurveillance and reconnaissance may be provided to the ground station258. The ground station may be a small portable device 259, such as amobile phone or PDA, authorised users may control the aerial vehicle bysimply specifying a location of interest, the autopilot will then plot acourse to this and provide appropriate feeds from sensors to the userthat may include providing services. Services provided by the Aerialvehicle may include: data networking, broadcasting it's location withembedded timecoding for positioning systems, transmitting the locationof objects of interest (e.g. AIS), radio communication to a requiredstandard. These services may be provided to a wide area that may be 100square miles or more for each aerial vehicle or highly localised, thisis achieved with of one or more parabolic mirrors or lens to alter thetransmission to a wide or narrow coverage area. Additionally, the aerialvehicle may relay communication at a higher signal strength or utiliseanother standard, for example a voice call may be made using a mobilephone which is then transmitted to a satellite, allowing a user toaccess other networks without in this case having to use a satellitephone. A command and control centre 231 e, may direct or control thevehicle and receive sensor feeds or access the databases 21 through 216.Additionally the command centre may also specify that alerts areprovided for a given set of conditions, for example, a motor car that isexceeding the speed limit. A material with an explosive chemical makeupbeing identified in the air or a particular vehicle type entering anarea of interest. A Safety pilot remote control 260 may allow thevehicle to be operated in civilian airspace or to pilot the vehicledirectly from a remote location. A master vehicle 261 may co-ordinatethe positions of one or more slave vehicle to maintain a honeycomb meshdata network. A ship 262 may broadcast an AIS signature to the vehicle,that may be relayed allowing the position of the vessel to be known wellbeyond the normal range of a surface based transmitter. Similarly othervessels that are not equipped with AIS may be identified and theirposition broadcast across the AIS network. Air traffic control 263 maydirect a vehicle directly or provide updated aircraft positions. Anaircraft 264 may broadcast its position, bearing and speed to thevehicle.

A ground based light 231 g may be controlled and orientated by theaerial vehicle to point towards it and the solar cells 201 orientated233 b towards the light source, unusually the solar cells may beorientated downwards towards earth to receive light from the groundlight. This allows additional energy to be provided to the vehicle inlow lighting conditions such as winter. Typically the light will beturned on before dusk when light is emitted in the visual spectrum, butmay be turned on when required if transmitting outside the visual lightspectrum.

FIG. 15 depicts an alternative embodiment of the present invention. Theconstruction is the same as the embodiment of FIG. 1, apart from thedescription below. In this embodiment the actuated control rod 1500, hasa cylindrical control surface 1502 that may provide additional force toorientate the vehicle. The cylindrical control surface 1502 is held inposition with struts 1501 that are ideally a symmetrical aerofoil crosssection and made of carbon fibre reinforced composite. A lightning rod1503 is provided, ideally made of a carbon fibre reinforced compositetube with a symmetrical aerofoil cross section into which is placed aconductive wire of silver. Should lightning strike the vehicle, thelightning rod is communicated this electrical energy though theconductor as to not disrupt or damage electrical system operation.Actuated parabolic mirrors 1504 are provided and described further inFIG. 15C, 15D, 15E, 15F, 15G and 15H. The parabolic mirrors 1504 a maybe orientated to receive and transmit a radio transmission from anotherstation as illustrated by 1505. Similarly another parabolic mirror 1504b may be orientated towards the ground to receive light from a groundbased light 1506. The vehicle has a hydrogen storage chamber 1499, thatcan be presented to a fuel cell to produce electrical power or used asfuel to power an engine, such as a wankel or reciprocating engine, todrive the pump 242 or a conventional method of propulsion to providebursts of speed to assume a loitering position (not shown). Conventionalmethods of propulsion may include a propeller or jet engine. Thehydrogen storage chamber is preferably cylindrical or spherical and maybe constructed of fibre reinforced polymer composite or light weightmetal or metal alloys, including aluminium or titanium.

FIG. 15 a illustrates the ground based light, that comprises a lightemitter 1509. Light emitted 1509 may be a flood light or an lightemitter beyond the visual spectrum, such as an infrared LED, that emitslight ideally between the 700 to 3000 nanometer range. The light isdirected to the vehicle using a parabolic mirror or lens to produce ashaft of light. Alternatively a coherent light source may be used, suchas a laser. A megatron that produces light in the microwave range mayalso be used (but not preferred). By example, a 10 kW light sourceemitting light for 1 hour (assuming 90% optical losses in theatmosphere) is sufficient to sustain the airframe at a groundspeed(excluding wind) of around 75 kms/hr throughout the night, in the monthof December in London, England. In the case of a fixed position groundlight, the absolute position of the ground light is known (it may alsobe transmitted to the vehicle for movable surface lights) the requiredorientation is calculated and transmitted to the light source 1506.Servos 1507 and 1508 orientate the light and emit light 1509 on demandto the aerial vehicle. These are received by concentrated solar panelcollector on the vehicle 1504 b. The light ground station may be poweredby solar power and installed on a buoyant platform that may be tetheredfor oceanic applications.

FIG. 15 b shows an alternative embodiment, where the first liftcompartment 1511 is positioned to the front and rear of the vehicle andsecondary ballast compartment 1512 is presented in the middle of thevehicle around the wing. A lighting rod 1513 is situated at the midpoint (previously described) but extends around the main fuselage.

FIG. 15 c represents a detailed perspective view of an alternativeembodiment of the solar cell collector 1504 illustrated on FIG. 15. Afilm sleeve 1514 is bonded to the outer envelope, a carbon fibre member1515 is inserted to hold the mechanism and houses a pivot 1516. Aactuator 1518 rotates an outer carbon fibre ring 1517 to achieve yaw. Asecond actuator 1519 achieves pitch to rotate an inner carbon fibre ring1520. A parabolic mirror is made of mirror film (described above),mirror film sections 1522 a are bonded to a centre section 1521 andattached to the inner carbon fibre ring 1520 with an adhesive. Anoptional outer mirror film ring 1523 may be added. The mirror filmscreate a parabolic mirror 1529 as shown in FIG. 15D in cross section. Acarbon fibre member 1524 holds a solar cell 1526 and corrective mirror1525 in position. Ideally the corrective mirror is a silverised mirrorfoil, such as Silver Miro supplied by Alanod of Germany. The solar cellis ideally a high efficiency concentrator photovoltaic cell previouslydescribed, but may be any PV cell that creates electrical energy fromsunlight. An additional linear actuator 1528 may be used to control thefocal point of a radio transmitter/antenna 1527. FIG. 15D shows incominglight 1530 being reflected from the parabolic mirror 1529 and acorrective mirror 1525 into the solar cell 1526. FIG. 15E in perspectiveview and 15F in cross sectional view show an alternative cassegrainembodiment. Light 1530 is reflected from the film mirror 1522 b onto asecondary mirror 1525 and into a solar cell 1526. FIG. 15F inperspective view and 15G in cross sectional view, show an alternativeoff-centre parabolic embodiment.

FIG. 16 depicts an alternative embodiment of the present invention. Theconstruction is the same as the embodiment of FIG. 1, apart from asdescribed below. In this embodiment the solar cell arrangement isconfigured so that the mirror film 1602 can move independently of thesolar cell 1604. FIG. 16A depicts a cross section through the solar cellarrangement, showing how the solar cell 1604 is located around thecentral axis of the vehicle. This is enabled by a central channelrunning along the length of the vehicle along its main axis. The centralchannel is depicted in the cross section of FIG. 16B. The mirror film1602 rotates around the aperture. The solar cell 1604 rotatesindependently of the mirror film 1604 from within the aperture. Thisallows cooling of the solar cell.

FIG. 17 depicts a further embodiment of an aerial vehicle according tothe present invention. The construction is the same as the embodiment ofFIG. 1, expect as described below. This embodiment includes a drogue oranchor that can be released to drag in a body of water below thevehicle, for example the sea or a lake or river. This embodiment isparticularly useful to maintain a position against strong winds, or forapplications by the coast guard or for oceanic operators. The use of thedrogue can enable the vehicle to maintain a height below 60 m—necessaryif the vehicle is used as an unmanned aerial vehicle under an autopilotin UK airspace. Territorial airspace extends twenty four nautical milesfrom the coastline—at that distance a higher altitude can be used. Aconventional propeller 99 may be used to achieve steady, level flight atlow altitude. The drogue creates significant drag in water to keep thevehicle in position in high wind for oceanic applications, savingsignificant energy that would otherwise be required for propulsion tokeep the unit at station. Typically, the unit drifts with the use of adrogue by 1/30^(th) the distance compared to not using the drogue.

The vehicle comprises an aerodynamic compartment 94 (preferably foam)with plastic film skin. This compartment includes an actuator that maybe a winch servo 95 to retract or deploy the tether line 100 and an IRemitter 96 for communication with the drogue 105. Towards the rear is apermanent magnet 97 which mates with the drogue magnet 102 so that whenit is not in use it is maintained close to the body of the vehicle witha carbon fibre member 104. When required, the drogue 105 is released byoperating a electromagnet 98.

This embodiment includes a propeller 99 at the rear of the vehicle. Thepropeller is driven by a motor. It is provided to assist flight at lowaltitude, for example 60 m or lower, where the buoyancy method ofpropulsion cannot be used as efficiently because of the small verticalrange available.

The drogue 105 is connected to the vehicle by a tether line 100. Adrogue control unit 101 is attached to the bottom of the tether line100. The outer surface of the control unit 101 is a solar panel tocharge the unit. Drogue unit tether lines 105 a extend from the controlunit 101. A retraction line 106 is also provided. The drogue includes apermanent magnet 102 mounted on a carbon fibre strip 104 that fits theprofile of vehicle when the drogue is not deployed. The drogue 105itself is made of a thick grade of polymer film described above. In FIG.17 the drogue is shown deployed below a water level 1700.

FIG. 17A depicts the control architecture for the drogue 105. Itincludes a battery 107, IR receiver 108, Winch servo 109 and solar panelbody 110.

Another embodiment of the invention is depicted in FIG. 18. Thisembodiment is identical to the embodiment of FIG. 1, except as describedbelow. In this embodiment a wing extends between two or more nacelles ateach side of the vehicle.

A wing, which can have profiles as described above, supports a solarcell 111 on its upper surface (and lower surfaces in some embodiments).An opening is formed in the solar cell 111 in which is suspended asymmetrical aerofoil payload section 113 by lines 112. The payloadsection carries batteries and winch servos that can move the payloadaround to move the centre of gravity of the vehicle to orientate andcontrol the vehicle. As depicted in FIG. 18, the nacelles 1799 at eachside of the vehicle do not contain a solar cell arrangement, although inalternate embodiments this may be provided instead of or in addition tothe solar cell 111. The nacelles include a pump 114 for filling theballast chambers.

The wingspan carbon fibre section used in the embodiment of FIG. 1 maybe used in this configuration on the leading and trailing edge to reducebending across the wing (indicated generally by numeral 115).

Thus, according to the invention, the vehicle comprises a main nacelleor nacelles with rudder and elevators. The rudder and elevators arepreferably made of a carbon fibre frame (water-jet cut sheet), filmcovers the frame. The rudder is preferably actuated at the centre ofpressure so that a small servo can be used. The servo is preferablyhoused in the rear polystyrene compartment that also houses the controlunit, GPS unit, transmitted/received and other antenna. The polystyrenecontainer may have a carbon fibre cap with a tail running along the rearcompartment to provide additional stability for the control surfaces. Afilm nacelle envelope covers the cap and is preferably secured with areinforced composite of fibre and resin to provide an air tight seal,that may be secured with a fixture.

The main nacelle is preferably made of EVAL (Ethylene Vinyl-AlcoholCo-polymer) barrier between one or more polymer films with an additionalceramic coating. The barrier film composite has a low demonstratedhelium permeability of 160 cc/m²/atm/24 hrs without an additionalceramic coating. Eight sections of film make up the nacelle section,which may be bonded with an ultrasonic/radio frequency welding machineto provide a good seal. The seams are reinforced on the reverse of theseal with fibre reinforced tape to provide a strong joint. EVAL offers100 times less helium permeability compared with Mylar. This wouldresult in helium loss of 6.91 cc/m²/ATM/hr through the film, or 0.943l/day for the preferred and exemplary embodiment.

For the embodiment of FIG. 1, this provides a theoretical lift enduranceof 239 days with a 50% loss of free lift, resulting in reducing theupper operating altitude from 3 km to around 2 km.

Solar energy is reflected using a parabolic mirror made of mirror filmin the solar cell arrangement. The film is preferably adhered to acarbon fibre frame at each end. Servos orientate the solar trough toharvest available sunlight. Sunlight is concentrated onto a photovoltaicreceiver, facing towards the mirror film. The photovoltaic cell isattached to the carbon fibre frame and the top section (not shown) ismade of mirror film which reduces heat build-up on the reverse of thephotovoltaic film and maintains the elliptical profile of solar filmacross its length. This arrangement reduces the overall mass of thecraft and also allows the sun's path to be tracked, maximising energyyield.

The component compartment is preferably made of polystyrene andencapsulated in Mylar film, it may house a winch servo to move thecomponent compartment forward and aft, moving the mass along the mainaxis of the craft to provide pitch control. A servo moves the battery ina perpendicular horizontal plane to the main axis, to provide rollcontrol. The waste heat from the pump keeps the batteries withinoperating temperature range. The pump is preferably also housed withinthe polystyrene container and connected to a solenoid valve. Ventilationand a Mu metal foil draw heat away from the pump when in operation. Apipe draws in atmospheric air to the pump and two pipes run the lengthof the craft to the air ballast chambers.

As atmospheric air is pumped, water builds up in the feed pipes. Thiswater is collected in a container attached to the feed pipes and mayeither be purged when the valve is switched or presented to anelectrolysis unit for processing into hydrogen to replace helium liftgas lost through the envelope. To replace 40 cc of helium lost per hourwill require electrolysis of 0.7 cc of water per day, to liberatehydrogen to replace the lost lift gas.

The endurance of the Aerial Buoyancy Glider is unlikely to be limited bylighter-than-air gas loss, but more likely the effective batteryrecharge cycles. Lithium Sulphur batteries are preferred as they havethe highest specific energy per kilogram (350 Wh/kg, 260 Wh/kg realisedat the pack level). However, the recharge cycles are likely to be only60-90 cycles. Alternatively, Lithium Polymer batteries would offer anattractive alternative for longer term (1000 cycles+, with a lowerspecific energy of 206 Wh/kg). Other battery technologies may also beused, such as lithium air that may offer higher specific energies.

The wings extend from main compartment, but may be combined in someembodiments

Having described the construction of various embodiments, the principleof operation of the present invention will now be discussed. The presentinvention derives motion from alternating upward and downward movements.The vehicle rises under a buoyancy force resulting from the lift gascontained within the first compartment. The vehicle falls by increasingits mass by pumping atmospheric air as ballast into the ballastcompartments. It can then rise by expelling the air compressed in theballast chambers.

During the upward and downward motion the orientation of the vehicle iscontrolled such that a horizontal motion component arises. For examplethis may arise by force provided by a wing, or by the shape of the mainbody of the vehicle itself. The resulting motion resembles a “zigzag” or“saw tooth” when viewed from the side. The motion is depicted in FIG.19.

The vehicle may alter this gliding path over this cycle to minimiseenergy usage (typically a longer gliding inflection with a longergliding distance) or increasing airspeed (typically a shorter glidinginflection with shorter gliding distance). The gliding angle may also bechanged throughout this cycle to maximise ground speed or energy usage.

The vehicle operates over an altitude range 1800, which is typically 2km or more in a preferred embodiment. The altitude range has an upperlimit 1802 and lower limit 1804 above the ground level 1806. In apreferred embodiment the upper limit 1820 is 3 km or more above groundlevel and the lower limit 1804 is 1 km or less above ground level. Thevolume of the main compartment of the vehicle containing the lift gaswill determine the buoyancy of the vehicle and the overall buoyancyceiling 1808 where the density of the vehicle equals the density of thesurrounding air. The vehicle may rise above the buoyancy ceiling bycircling on thermals 1810 in the same way as gliders, if thermals areavailable.

The method of the present invention uses buoyancy to translate avertical force to horizontal and vertical force components through thewing giving ground speed. In a preferred embodiment the overall mass ofthe vehicle is 1.7 kg with 2.3 m³ of helium generating free lift of0.712 kg at sea level. As the glider rises through the atmosphere, theair density decreases reducing buoyancy, resulting in free lift of 0.489kgs at 1000 m altitude, falling to 0.09 kg of free lift at 3000 m. FIG.20 shows ground speeds for various gliding ascent inclinations.

As the glider ascends, the control surfaces are orientated and/orinternal masses are repositioned to change the centre ofgravity/buoyancy to orientate the craft at the desired glide angle. Atthe top of the ascent, a gas pump draws in atmospheric air which isstored in the air ballast chambers located at the front and rear of thevehicle.

The ballast compression chambers have a combined volume of 0.46 m³ inthe preferred embodiment and can withstand a pressure of up to 3.8 Atm,though typically pressurised to a differential pressure of 1.5 Atm. Asuitable pump may be fabricated using light weight components with aweight of only 500 grams.

The pump's performance varies with the differential pressure between theatmospheric air drawn in and output pressure of the compression chamber,pumping 120 litres/min at atmospheric pressure, falling to 40 litres permin under 1.5 Atm differential pressure. Air ballast may accumulate at arate of around 100 grams per minute at the beginning of the glidingdescent; however this is offset by the increase in buoyancy as the craftfalls. The pump must therefore pump sufficient atmospheric air to offsetthe increase in buoyancy to maintain a heavier-than-air state to achievea gliding descent, as shown in FIG. 21.

At the bottom of the gliding descent, a valve is opened, allowing airballast held in the compression chamber to be expelled. It is importantto note that some pressure is held within the air compression chamber sothat the chamber is fully inflated. The valve is pulsed to keep the aircompression chamber pressure above atmospheric pressure throughout theascent glide.

The preferred embodiment is designed to operate within a 1-3 km altituderange, however if thermals are available, the glider can circle toobtain greater altitude. Other operating ranges can also be used, forexample changing the mass of the vehicle or increasing the volume oflift gas to extend this operating altitude range.

Should wind offer useful assistance, then it may be utilised. This isparticularly relevant for travelling to a desired destination. Altitudewind measurements may be gathered and transmitted to other aerialbuoyancy gliders for this purpose.

The vehicle can attain altitudes considerably higher than the buoyancyceiling of 3.5 km by utilising thermals, ridge lift, or lee waves. Thiswould allow high speed winds to be utilised to travel considerabledistance at speeds beyond the method of buoyancy propulsion alone, notnecessarily a straight line flight path to the destination. Inparticular it is envisaged that jet streams may be utilised in someembodiments.

The aerodynamic model utilised to control the vehicle of the inventionand the method of flight will now be discussed with reference to theembodiment of FIG. 1. For the sake of illustration the lift and dragcoefficients for the lift nacelle are taken from Online Panel Codes fora LWK 100-80, Department of Aeronautics and Astronautics, Naval PostGraduate School, United States Navy. The lift and drag coefficients forwing are based on a flat plate.

C _(dα)=1.28 sin α

C _(lα)=2πα  (1)

The total drag takes into account vortex/induced drag at small angles ofattack. The aspect ratio for the wing is 6 (with a 0.3 taper ratio) and0.068 for the nacelle. e is the elliptical factor, assumed to be 0.95for the wing (which is a reasonable for a wing of this aspect ratio andtaper) and 1.0 for the nacelle, as it is a good elliptical shape.

C _(Dα) =C _(dα) +C _(di)(C ₁ ² /πeAR)  (2)

The angle of attack (αeq) is derived from the equilibrium glide angle,which varies between 0.07° to 0.00096° for glide angles of 8.8° to 58°,respectively. FIG. 22 depicts an equilibrium gliding descent and FIG. 23depicts and equilibrium gliding ascent.

The coefficients are based on planform areas of 3.187498 m² and 4.68 m²for the nacelle and wing, respectively. The total airframes coefficientsare the average of the nacelle and wing (excludes the control surfaces).The low CD is a result of not needing to create aerodynamic lift, otherthan to keep the vehicle on the glide flight path. FIG. 24 shows thelift and drag coefficients with angle of attack.

The minimum glide path angle is achieved at L/Dmax:

$\begin{matrix}{{\tan \; \gamma_{\min}} = {{- \frac{C_{D\; \alpha}}{C_{L\; \alpha}}} = {{- \frac{0.001235}{0.007981}} = {{0.15478\therefore\gamma} = {8.8{^\circ}}}}}} & (3)\end{matrix}$

The airspeed is derived at the equilibrium glide angle. In this case,the minimum glide angle.

$\begin{matrix}{V_{glide} = {\sqrt{\frac{2W}{\rho_{2000m}S_{1}\sqrt{C_{D}^{2} + C_{L}^{2}}}} = {11.02\mspace{14mu} {m/s}}}} & (4)\end{matrix}$

The LWK 80-100 is used as a reference aerofoil. Other aerofoils may alsobe used. At small angles of attack, little aerodynamic lift (negativelift on a gliding ascent) is generated and the associated vortex/induceddrag is minimal.

In summary, the vehicle is a lightweight hybrid aircraft that uses abuoyancy engine to translate a vertical force to horizontal and verticalforce components through a fixed flat plate film wing. The glider hassufficient airspeed to penetrate winds that may be encountered (otherthan the most extreme winds), offers a very efficient method ofpropulsion and may harvest sufficient solar energy to power on-boardsystems at most global locations throughout the year (at an approximateLatitude range ±56°). The unit may effectively operate at latitudes ±57°to ±63° for 10 months of the year and ±64° to poles for 6/8 months ofthe year.

Possible applications of the vehicle will now be discussed. The vehicleis an inexpensive platform, with very long endurance and as such,provides a near permanent aerial platform for Earth observation andnetworking.

The vehicle provides a useful persistent aerial platform for scientificsensors, meteorological data gathering and imaging equipment (including;Synthetic Aperture RADAR, high resolution optical camera and infraredcamera). The vehicles may either loiter over a single location toprovide on-going situational awareness or survey wide areas. Workingautonomously, the vehicles do not necessarily require a manned groundstation, can operate for months at a time, needing minimal supportinfrastructure and do not require a landing runway when scheduledmaintenance is required.

By way of illustration, commercial-off-the-shelf CISCO equipment can beused to create an aerial IP based network access point. A number ofvehicles may be deployed in a honeycomb formation as shown in FIG. 25.

For a high bandwidth network, a distance of 5 km between vehicles canprovide a bandwidth of 48 Mbs. Bandwidth falls off to 11 Mbs at 16 kmand 2 Mbs at 25 km distance between nodes.

By way of example, fifteen vehicles may provide blanket wi-fi accessacross Greater London. For oceanic networking, a persistentover-the-horizon data network would be desirable for ship-to-ship andship-to-shore communication that does not require expensivegeo-stationary satellite communication usage.

Bandwidths can be significantly increased for point-to-pointcommunication.

The vehicle's weight is typically 1.7 kgs to 3 kgs packaged weight(approximately the size of a one-man tent). When the unit is deployed,the envelope is unfolded, the wingspan sections attached and the mainenvelope inflated from a lighter than air gas canister, such as helium.The vehicle does not require a bulky launch catapult or runway and maybe launched from a small navel ship or practically anywhere in thefield. For advanced deployed units, it is noted that pressurised heliumshould not be carried onboard an aircraft and an off-the-shelfelectrolysis unit may be used to inflate the glider with hydrogen.

The vehicle typically operates at an altitude of 1-3 km, but may operateat much higher altitudes by utilising thermals or an alternativeembodiment that generates more freelift. The envelope and wing aretransparent, the solar cell arrangement may be printed on the reverse toreduce its visual footprint. The unit operates beyond the range ofground rifle fire. The vehicle flies silently and offers minimal cluesto its presence from the ground. The vehicle has minimal thermalsignature and has ‘bird-like’ radar signature and flightcharacteristics.

A Kestrel autopilot commercially available from Procerus Technologies,500 South Geneva Road, Vineyard, Utah 84058, USA may be used, providingautonomous flight operation with seamless camera alignment, e.g. theunit does not need to be piloted and aerial imagery is provided onrequest by simply specifying a co-ordinate, the autopilot takes care ofthe rest.

An easy field implementation would be to use a wi-fi enabled ‘smartphone’ to request aerial Intelligence, Surveillance and Reconnaissance(ISR) with ongoing situational updates provided on-screen or otherservices described above, thus an aerial unit may be under the directguidance of a small unit. The vehicle provides the network access pointand the ISR. In the context of a field-wide network, the ISR feed may beprovided to command for further image processing and objects of interestidentified and, where applicable, concise situational updates providedto the required field personnel.

If the vehicles operate in non-military airspace, then they can bepiloted. The autopilot allows multiple craft to be operated by a singlepilot. With further development, it is envisaged that the guidancesystem could include consideration of:—

-   -   Dynamic global 3D wind map    -   Prediction of the likely occurrence of thermals from the lie of        the land and time of day    -   Optimise aerial energy sources (thermals, glide path, high speed        winds and solar energy)

The vehicle has endurance well beyond the current generation of tacticalUnmanned Air Vehicles (UAVs), which require readying, piloting to arequired position to obtain limited ISR, piloting back to a groundstation, recovery and servicing. The vehicle simply remains at aloitering station providing ongoing ISR and radio communicationservices. Other aircraft may be more capable in terms of airspeed,operating altitude and sensor ranges, however, they require considerablemanpower to operate, have a significantly higher capital cost,associated running costs and need to be refuelled and ultimately landfor maintenance which can be both time consuming and costly. Monitoringthe routes used by Military ground vehicles and convoys is a singlefunction the vehicles may perform amongst many other useful roles.

The vehicle offers a very low cost, persistent aerial platform with verylong endurance. As the vehicle operates at a low operating altitude,less power hungry sensors and communication equipment can be used. Adhoc aerial networks are known, offering line-of-sight radiocommunication to a ground receiving station. Aerial assets form ad hocconnections between nodes, however, these networks can only take placeif an aircraft is over a particular location. If there are no aircraftin the sky, there is no network. The vehicles would allow a plannednetwork to be established over a very wide area, with consistentbandwidth and access.

The vehicle is well suited to an IP based network infrastructure. Thevehicles would allow a low-cost field-wide IP based network to beprovided alongside the existing infrastructure and facilitate a highbandwith global telecommunication network.

A unique feature of the vehicle is that the vehicle may land on a bodyof water or deploy and recover sensors. For example, make an activesonar sounding and undertake another sounding elsewhere without thelocation of the host control vessel being determined. Additionally, thevehicle could be used in international waters to monitor merchant shipsand interests, covering a wide patrol area. There has been an increasein Pirate activity off Somalia (the significant coastline is around 1000km), with 93 attacks reported in 2008. Around 20 vehicles could providenetworked surveillance of this coast, to detect any ships entering theshipping lanes. The location of all ships could then be passed acrossthe AIS network to all merchant ships in the area and the position ofsuspicious vessels passed to NATO Naval vessels in the vicinity forfurther investigation.

1. An aerial vehicle comprising: a first compartment for holding alighter than air gas; a second compartment for holding atmospheric airand having an inlet and an outlet; a solar panel for converting sunlightinto electricity; a compressor for pumping atmospheric air through theinlet into the second compartment; control means for controlling thepitch and yaw of the vehicle; and a controller for controlling thebuoyancy of the vehicle via the compressor and the outlet such that thevehicle is either lighter than the surrounding air and rising or heavierthan the surrounding air and falling, and for controlling the controlmeans such that the rising and falling motion includes a horizontalcomponent.
 2. An aerial vehicle comprising: a first compartment forholding a lighter than air gas; a second compartment for holdingatmospheric air and having an inlet and an outlet; an engine; a fueltank for storing fuel for use by the engine; a compressor for pumpingatmospheric air through the inlet into the second compartment; controlmeans for controlling the pitch and yaw of the vehicle; and a controllerfor controlling the buoyancy of the vehicle via the compressor and theoutlet such that the vehicle is either lighter than the surrounding airand rising or heavier than the surrounding air and falling, and forcontrolling the control means such that the rising and falling motionincludes a horizontal component.
 3. (canceled)
 4. An aerial vehicleaccording to claim 1, wherein the aerial vehicle creates substantiallyno aerodynamic lift at a zero degree angle of attack.
 5. An aerialvehicle according to claim 1, wherein the aerial vehicle furthercomprises a nacelle, and wherein the first compartment and the secondcompartment are both contained within the nacelle.
 6. An aerial vehicleaccording to claim 5, wherein the nacelle has an outer surface whichdefines a body of revolution or an aerofoil.
 7. An aerial vehicleaccording to claim 5, wherein the nacelle is transparent and the solarpanel is contained within the nacelle.
 8. An aerial vehicle according toclaim 5, further comprising a parabolic mirror associated with the solarpanel for focussing sunlight onto the solar panel.
 9. An aerial vehicleaccording to claim 7, further comprising an actuator for changing theorientation of the solar panel and/or the parabolic mirror relative tothe vehicle.
 10. An aerial vehicle according to claim 1, furthercomprising at least one wing.
 11. An aerial vehicle according to claim10, wherein the at least one wing comprises the solar panel.
 12. Anaerial vehicle according to claim 11, wherein the solar panel ispositioned on the underside of the at least one wing.
 13. An aerialvehicle according to claim 1, wherein the nacelle is an aerofoil with aratio of thickness to chord length between approximately 5% andapproximately 35%.
 14. An aerial vehicle according to claim 1, wherein awall of the first compartment may comprise a barrier layer for limitingloss of the lighter than air gas through the wall of the compartment.15. An aerial vehicle according to claim 1, further comprising a thirdcompartment for holding a refrigerant which can undergo a reversiblephase change from a gas into a liquid.
 16. (canceled)
 17. An aerialvehicle according to claim 1, further comprising at least onetransmitter and at least one receiver for providing a wirelesscommunications network.
 18. (canceled)
 19. An aerial vehicle accordingto claim 17, wherein the at least one receiver comprises an antennaformed by a metallised track having an undulating pattern. 20.(canceled)
 21. An aerial vehicle according to claim 1, wherein thecontrol means comprises a movable mass.
 22. An aerial vehicle accordingto claim 1, further comprising an electrolyser for electrolysing waterinto hydrogen and oxygen.
 23. (canceled)
 24. An aerial vehicle systemcomprising: an aerial vehicle according to claim 1; and anelectromagnetic radiation source for emitting electromagnetic radiationfor reception by the solar panel.
 25. (canceled)
 26. (canceled)
 27. Amethod of flight for an aerial vehicle comprising a first compartmentfilled with a lighter than air gas and a second compartment for holdingatmospheric air, the method comprising: alternately compressingatmospheric air into the second compartment and then releasing thecompressed atmospheric air from the second compartment, thereby alteringthe buoyancy of the aerial vehicle such that it is either heavier thanair and falling or lighter than air and rising; and actuating at leastone control surface such that the rising and falling motion includes ahorizontal component.